1. Field of the Invention
This invention relates to producing clean and dry glass powder from unsorted post-consumer waste glass and its use in applications including, but not limited to, concrete mixes, paint additives, and filler media.
2. State of the Art
Glass powder has been produced for years in limited quantities and is available to some extent for industrial applications. At present, glass powder is created from fiberglass raw material rejects and industrial waste from a fiberglass manufacturing operation, both of which are available in only selected locations. Increasing transportation costs have made it desirable to use glass that is available locally. This fact, and the glut of post-consumer waste glass available, makes post-consumer waste glass a logical choice for manufacture of glass powder. However, post-consumer waste glass has drawbacks as a feedstock, in particular its tendency to be contaminated with various foodstuffs and chemical residues, and to be mixed with trash, including labels and other paper scraps, as well as ceramic, plastic, and metal items of various sorts. These issues must be addressed and overcome in order to process post-consumer waste glass into usable glass powder in industrial quantities.
More specifically, for some years it has been commonplace for consumers to be expected to sort out empty glass containers for recycling. Ideally, this waste glass would be recycled as new containers. However, post-consumer waste glass is most often produced in various colors (clear, green, and brown being the most common) and cannot be sorted economically either manually or by automated equipment. Moreover, post-consumer waste glass tends to be mixed with plastic and ceramic waste, as well as undifferentiated trash. The difficulty of separating the glass from these other materials and separating the glass into its various colors has precluded efficient recycling of glass into new containers; as a result, most waste glass is now disposed of in landfills, a highly inefficient and undesirable end for this valuable material.
At the same time, it is known that under proper circumstances glass powder can serve as a substitute for some fraction of the Portland cement commonly used in concrete. While large glass particles are undesired as a component in concrete, due to a well-known alkali-silicate reaction (ASR) occurring between the alkalis of the glass and the silica of the aggregate components of the concrete, which weakens the concrete, it is known that when the glass is powdered it behaves as a pozzolanic material, that is, will exhibit a cementing property when mixed into a moistened mixture having a very high pH (e.g., 12.5). See, for example, Shayan, Value-Added Utilisation of Waste Glass in Concrete, IABSE Symposium Melbourne 2002; Use of Recycled Glass for Concrete Masonry Blocks, Carver et al, NYSERDA Report 97-15 (1997). Portland cement is in short supply from time to time. Accordingly it would be desirable if an efficient process for making high-quality, clean, dry powdered glass from post-consumer waste glass could be provided. The powdered glass thus made could be used in partial substitution for Portland cement in concrete and in other applications now known for powdered glass, e.g., paints and fillers for various products and uses.
U.S. Pat. No. 6,296,699 to Jin for “Inorganic binders employing waste glass” discusses using waste glass powder in concrete and “artificial stone”. An alkali metal activator, for example, an alkali metal hydroxide, silicate, aluminate, carbonate, sulfate, phosphate or fluoride is mixed with the glass powder and water, and this material is cured, in some examples at room temperature. Jin teaches that the waste glass should be cleaned in advance to remove residues such as sugar from the waste glass which can affect the setting and binding of the concrete. He further states that the processes used to create glass powder from waste glass, e.g., ball milling and pulverizing, are well known.
In a report titled “Recycling of Crushed Glass into Coating Products”, CWC Report No. GL-96-1 (1998) the authors state that “paint and coating applications are especially sensitive to organic contamination. For example, one unwashed jar of mayonnaise could provide enough residue to bacterially contaminate many gallons of paint.”
Vitunac et al U.S. Pat. Nos. 5,350,121 and 5,246,174 show methods for recycling glass, directed primarily to recycling of TV picture tubes, with much attention to removing heavy metals, coatings and the like. Pulverizing, washing, rinsing and further crushing steps are disclosed generally.
Abernathy U.S. Pat. No. 4,030,670 shows a trash recycling system including separation of various sorts of trash. Glass fragments are washed and dried.
Morey et al U.S. Pat. No. 4,067,502 and Morey U.S. Pat. No. 4,070,273 show flotation separation of glass fragments (up to 10 mesh) using amines as beneficiation agents.
Baxter U.S. Pat. No. 5,803,960 shows making glass for concrete reinforcement, while avoiding the alkali-silica reaction (ASR) by mixing a lithium-containing composition with crushed bottle glass. The glass may be provided in powder or fibrous form. Baxter et al U.S. Pat. No. 5,810,921 shows a similar invention using chromium instead of lithium.
Pelot et al U.S. Pat. Nos. 6,344,081 and 6,699,321 show concrete compositions, and emphasize the use of “electric” or “E-glass” powder of between 100 and 325 mesh in concrete. The claims require the glass particles to be no larger than 80-120 mesh, 40-60% between 180 and 220 mesh, and 10-30% less than 325 mesh; the cement used is to be low-alkali. The glass is to comprise up to 25% of the mix.
Bergart U.S. Pat. Nos. 5,950,936 and 6,168,102 show a system for recycling glass from a post-consumer waste glass stream including other sorts of debris. The process steps include various sorting, screening, crushing, presoaking, washing, dewatering, and drying steps. If a glass powder is desired, second crushing and separation steps may be included. The dewatering step can be performed using a rotary screw conveyor (col. 4, line 32 of the '936 patent), and the drying step using a fluidized bed dryer (col. 4, line 44). It is acknowledged that some ceramic content will remain, and it is asserted that if the ceramic content is not acceptable to the end user, a second crushing stage can be performed to form a fine glass powder; the “ceramic particles dispersed throughout the glass powder will dissipate in further processing”. Col. 5, lines 48-52.
Kimmel et al U.S. Pat. No. 6,112,903 shows a method for sorting various types of glass from one another. A stream of glass cullet mixed with other items is heated using microwave energy; as different types of glass and items of other materials absorb different amounts of energy, they are differentially heated, and can be differentiated in a digital image made by a thermal imaging camera. A downstream diverter mechanism can then be used to separate out various constituents of the stream. Kimmel et al U.S. Pat. No. 6,464,082 shows a complete system employing this technique.
Harada U.S. Pat. Nos. 6,250,576 and 6,446,884 show a method and system for producing glass sands by crushing and agitating steps.
Sunde U.S. Pat. No. 6,743,287 shows a concrete using relatively large glass particles, requiring addition of a “non-alkali reactive mineral”, e.g. granite.
Whaley U.S. Pat. No. 6,770,328 shows a method of making a terrazzo surface using recycled glass in an epoxy matrix. Preparation of the glass is not discussed.
Thus, although the prior art discusses the use of waste glass powder in various applications, in particular as a partial substitute for cement in concrete, notes that post-consumer waste glass is not being efficiently utilized, and provides some suggestions for processes for recycling post-consumer waste glass, the art does not disclose a reliable and efficient process for the production of suitably cleaned and dried glass powder from post-consumer waste glass and the integration of that process into a process for the manufacture of concrete and concrete products, in particular one which does not require the addition of substances intended to suppress the alkali-silica reaction.